Inflammation is a complex process in which the body's defense system combats foreign entities. While the battle against foreign entities may be necessary for the body's survival, some defense systems improperly respond to foreign entities, even innocuous ones, as dangerous and thereby damage surrounding tissue in the ensuing battle.
Atopic allergy is an ecogenetic disorder, where genetic background dictates the response to environmental stimuli. The disorder is generally characterized by an increased ability of lymphocytes to produce IgE antibodies in response to ubiquitous antigens. Activation of the immune system by these antigens leads to allergic inflammation and may occur after ingestion, penetration through the skin, or after inhalation. When this immune activation occurs and pulmonary inflammation ensues this disorder is broadly characterized as asthma. Certain cells are critical to this inflammatory reaction and they include T cells and antigen presenting cells, B cells that produce IgE, and mast cells/basophils and eosinophils that bind IgE. These inflammatory cells accumulate at the site of allergic inflammation and the toxic products they release contribute to the tissue destruction related to the disorder.
While asthma is generally defined as an inflammatory disorder of the airways, clinical symptoms arise from intermittent air flow obstruction. It is a chronic disabling disorder that appears to be increasing in prevalence and severity.sup.1. It is estimated that 30-40% of the population suffer with atopic allergy, and 15% of children and 5% of adults in the population suffer from asthma..sup.1 Thus, an enormous burden is placed on our health care resources.
The mechanism of susceptibility to atopy and asthma remains unknown. Interestingly, while most individuals experience similar environmental exposures, only certain individuals develop atopic allergy and asthma. This hypersensitivity to environmental allergens known as "atopy" is often indicated by elevated serum IgE levels or abnormally great skin test response to allergens in atopic individuals as compared to nonatopics..sup.10 Strong evidence for a close relationship between atopic allergy and asthma is derived from the fact that most asthmatics have clinical and serologic evidence of atopy..sup.4-9 In particular, younger asthmatics have a high incidence of atopy..sup.10 In addition, immunologic factors associated with an increase in serum total IgE levels are very closely related to impaired pulmonary function..sup.3
Both the diagnosis and treatment of these disorders are problematic..sup.1 The assessment of inflamed lung tissue is often difficult, and frequently the source of the inflammation cannot be determined. Without knowledge of the source of the airway inflammation and protection from the inciting foreign environmental agent or agents, the inflammatory process cannot be interrupted. It is now generally accepted that failure to control the pulmonary inflammation leads to significant loss of lung function over time.
Current treatments suffer their own set of disadvantages. The main therapeutic agents, .beta. agonists, reduce the symptoms, i.e., transiently improve pulmonary functions, but do not affect the underlying inflammation so that lung tissue remains in jeopardy. In addition, constant use of .beta. agonists results in desensitization which reduces their efficacy and safety..sup.2 The agents that can diminish the underlying inflammation, the anti-inflammatory steroids, have their own known list of disadvantages that range from immunosuppression to bone loss..sup.2
Because of the problems associated with conventional therapies, alternative treatment strategies have been evaluated..sup.65-66 Glycophorin A,.sup.64 cyclosporin,.sup.65 and a nonapeptide fragment of IL-2,.sup.63 all inhibit interleukin-2 dependent T lymphocyte proliferation and therefore, IL-9 production,.sup.51 however, they are known to have many other effects..sup.2 For example, cyclosporin is used as a immunosuppressant after organ transplantation. While these agents may represent alternatives to steroids in the treatment of asthmatics,.sup.63-66 they inhibit interleukin-2 dependent T lymphocyte proliferation and potentially critical immune functions associated with homeostasis. What is needed in the art is the identification of a pathway critical to the development of asthma that explains the episodic nature of the disorder and the close association with allergy that is downstream of these critical immune functions. Nature demonstrated that this pathway is the appropriate target for therapy since biologic variability normally exists at this pathway and these individuals are otherwise generally not immunocompromised or ill except for their symptoms of atopy.
Because of the difficulties related to the diagnosis and treatment of asthma, the complex pathophysiology of this disorder is under intensive study. Although this disorder is heterogeneous and may be difficult to define because it can take many forms, certain features are found in common among asthmatics. Examples of such traits include elevated serum IgE levels, abnormal skin test response to allergen challenge, bronchial hyperresponsiveness [BHR], bronchodilator reversibility, and airflow obstruction..sup.3-10 These expressions of these asthma related phenotypes may be studied as quantitative or qualitative measures.
Elevated IgE levels are also closely correlated with BHR, a heightened bronchoconstrictor response to a variety of stimuli..sup.4,6,8,9 BHR is believed to reflect the presence of airway inflammation,.sup.6,8 and is considered a risk factor for asthma..sup.11-12 BHR is accompanied by bronchial inflammation and an allergic diathesis in asthmatic individuals..sup.13-21 Even in children with no symptoms of atopy and asthma, BHR is strongly associated with elevated IgE levels..sup.19
A number of studies document a heritable component to atopy and asthma..sup.4,10,21 However, family studies have been difficult to interpret since these disorders are significantly influenced by age and gender, as well as many environmental factors such as allergens, viral infections, and pollutants..sup.22-24 Moreover, because there is no known biochemical defect associated with susceptibility to these disorders, the mutant genes and their abnormal gene products can only be recognized by the anomalous phenotypes they produce. Thus, an important first step in isolating and characterizing a heritable component is identifying the chromosomal locations of the genes.
Cookson et al. provided the first description of a genetic localization for inherited atopy..sup.25 These investigators described evidence for genetic linkage between atopy and a single marker on a specific chromosomal region designated 11q13.1. Later, they suggested evidence of maternal inheritance for atopy at this locus..sup.26 Although maternal inheritance [genetic imprinting] had been observed for atopy, it had never been explained previously. However, efforts to confirm this linkage have not been generally successful..sup.27-31
Recently, the .beta. subunit of the high-affinity IgE receptor was mapped to chromosome 11q, and a putative mutation associated with atopy has been described in this gene..sup.32,33 However, because of the difficulties by others of replicating this linkage, the significance of this gene and polymorphism remains unclear. While additional studies will be required to confirm whether this putative mutation causes atopy in the general population, data collected so far suggests this polymorphism is unlikely to represent a frequent cause of atopy.
Because serum IgE levels are so closely associated with the onset and severity of allergy and asthma as clinical disorders, attention has focused on studies of the genetic regulation of serum total IgE levels. While past studies have provided evidence for Mendelian inheritance for serum total IgE levels,.sup.34-38 an indication of the existence of one regulatory gene, others have found evidence for polygenic inheritance of IgE, i.e., existence of several responsible genes..sup.39
Artisans have found several genes that may be important in the regulation of IgE and the development or progression of bronchial inflammation associated with asthma on chromosome 5q. They include genes encoding several interleukins, such as IL-3, IL-4, IL-5, IL-9, IL-13, granulocyte macrophage colony stimulating factor [GM CSF], a receptor for macrophage colony stimulating factor [CSF-1R], fibroblast growth factor acidic [FGFA], as well as others..sup.40 Recent evidence from family studies suggests genetic linkage between serum IgE levels and DNA markers in the region of these candidate genes on chromosome 5q..sup.41,42 Together, these investigations suggest that one or more major genes in the vicinity of the interleukin complex on chromosome 5q regulates a significant amount of the observed biologic variability in serum IgE that is likely to be important in the development of atopy and asthma.
Linkage [sib-pair analyses] was also used previously to identify a genetic localization for BHR..sup.79 Because BHR was known to be associated with a major gene for atopy, chromosomal regions reported to be important in the regulation of serum IgE levels were examined..sup.42 Candidate regions for atopy have been identified by linkage analyses. These studies identified the existence of a major gene for atopy on human chromosome 5q31-q33..sup.42
Therefore, to determine the chromosomal location of a gene[s] providing susceptibility to BHR, which would be coinherited with a major gene for atopy, experiments were carried out using linkage analyses between BHR and genetic markers on chromosome 5q..sup.42,79,82 Individuals with BHR were identified by responsiveness to histamine. Markers useful for mapping asthma-related genes are shown in FIG. 1.
Specifically, gene candidates for asthma, bronchial hyperresponsiveness, and atopy are shown [right] in their approximate location relative to the markers shown. The map includes the interleukin genes IL-4, IL-13, IL-5, and IL-3; CDC25, cell division cycle-25; CSF2, granulocyte-macrophage colony stimulating factor [GMCSF]; EGR1 early growth response gene-1; CD14, cell antigen 14; ADRB2, the .beta.2-adrenergic receptor; GRL1, lymphocyte-specific glucocorticoid receptor; PDGFR, platelet-derived growth factor receptor. Bands 5q31-q33 extend approximately from IL-4 to D5S410. The distances reported are sex-averaged recombination fractions.
Affected sib-pair analyses demonstrated statistically significant evidence for linkage between BHR and D5S436, D5S658, and several other markers located nearby on chromosome 5q31-q33..sup.79 These data strongly supported the hypothesis that one or more closely spaced gene[s] on chromosome 5q31-q33 determine susceptibility to BHR, atopy, and asthma..sup.79,80,81,82
Recently linkage has also been demonstrated between the asthma phenotype and genetic markers on chromosome 5q31-q33..sup.83 This region of the human genome was evaluated for linkage with asthma because of the large number of genes representing reasonable positional candidates for providing genetic susceptibility for atopy and BHR.
Linkage was demonstrated using the methods described above..sup.42,83 Specifically, 84 families were analyzed from the Netherlands with both sib-pair and LODs for markers from this same region of chromosome 5q previously shown to be linked to BHR and atopy..sup.42,83 An algorithm was used to categorize obstructive airways disease in the asthmatic probands and their families. This classification scheme was based, as described previously, on the presence or absence of BHR to histamine, respiratory symptoms, significant smoking history [&gt;5 pack years], atopy as defined by skin test response, airway obstruction [FEV1% predicted&lt;95% CI] and reversibility to a bronchodilator [&gt;9% predicted].
Evidence was found for linkage between asthma and markers on chromosome Sq by affected sib pair analysis (N=10, P&lt;0.05) and by maximum likelihood analysis with a dominant model for the asthma phenotype..sup.83
Asthma was linked to D5S658 with a maximal LOD of 3.64 at .theta.=0.03, using a dominant model [class 1 affected, class 2-4 uncertain, class 5 unaffected] with a gene frequency of 0.015 [prevalence of 3%]. A maximal LOD of 2.71 at .theta.=0.0 was observed for D5S470 which is approximately 5cM telomeric, or away from IL-9, relative to D5S436..sup.83
Subsequent to the original filing of this application, IL-9 or a gene nearby was suggested as likely to be important use atopy and asthma..sup.43 The IL-9 suggestion was based on a strong correlation in a randomly ascertained population between log serum total IgE levels and alleles of a genetic marker in the IL-9 gene..sup.43 This type of association with one or more specific alleles of a marker is termed "linkage disequilibrium", and generally suggests that a nearby gene determines the biologic variability under study..sup.44
The IL-9 gene has been mapped to the q31-q33 region of chromosome 5..sup.40 Only a single copy of the gene is found in the human genome..sup.45,46 Structural similarity has been observed for the human and murine IL-9 genes..sup.45,46 Each gene consists of five exons and four introns extending across approximately four Kb of DNA. Expression of the gene appears to be restricted to activated T cells..sup.45,46
The functions of IL-9 now extend well beyond those originally recognized. While IL-9 serves as a T cell growth factor, this cytokine is also known to mediate the growth of erythroid progenitors, B cells, mast cells, and fetal thymocytes..sup.45,46 IL-9 acts synergistically with IL-3 in causing mast cell activation and proliferation..sup.47 This cytokine also potentiates the IL-4 induced production of IgE, IgG, and IgM by normal human B lymphocytes..sup.48 IL-9 also potentiates the IL-4 induced release of IgE and IgG1 by murine B lymphocytes..sup.49 A critical role for IL-9 in the mucosal inflammatory response to parasitic infection has also been demonstrated..sup.50,51
In addition to IL-9, chromosome 5q bears numerous other gene candidates including IL-3, IRF1, EGR1, ITK, GRL1, ADRB2, CSF1R, FGFA, ITGA2, CD14, PDGFR, CDC25, CSF2, IL-4, IL-5, IL-12B, and IL-13. These may all be important in atopic allergy and as potential targets for therapeutic development. Moreover, the art lacks any knowledge regarding how the sequence of IL-9 or the function of IL-9 specifically correlates with atopic allergy, asthma, or bronchial hyperresponsiveness. Without such knowledge, artisans would not know how or whether to use IL-9 to either diagnose or treat these disorders.
The art does provide that IL-9 is a novel cytokine having an apparent molecular weight of approximately between 20 to 30 kD as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis under reducing conditions. It is produced as a 144 amino acid protein, that is processed to a 126 amino acid glycoprotein. Yang et al..sup.85 disclose that the DNA sequence encoding IL-9 comprises approximately 630 nucleotides, with approximately 450 nucleotides in the proper reading frame for the protein.
It is also known in the art that multiple protein isoforms may be generated from a single genetic locus by alternative splicing. Alternative splicing is an efficient mechanism by which multiple protein isoforms may be generated from a single genetic locus. Alternative splicing is used in terminally differentiated cells to reversibly modify protein expression without changing the genetic content of the cells. These protein isoforms are preferentially expressed in different tissues or during different states of cell differentiation or activation. Protein isoforms may have different functions and Alms and White have cloned and expressed a naturally occurring splice variant of IL-4, formed by the omission of exon 2, thus called IL-4.delta.2..sup.86 It was observed that IL-4.delta.2 inhibits T-cell proliferation induced by IL-4.
However, the art lacks any knowledge about IL-9 protein isoforms which are formed by deletions of exons 2 and 3 or the regulatory functions exhibited by these truncated proteins. Specifically, their role in regulating the biological activity, namely, the down-regulation of IL-9 expression or activity is unclear. Moreover, the formation of such isoforms by alternative splicing has not been previously observed or used to provide variants of IL-9 which function as agonists or antagonists of the native cytokine.
The art also lacks any knowledge about the role of the IL-9 receptor with asthma-related disorders. It is known that IL-9 binds to a specific receptor expressed on the surface of target cells..sup.46,52,53 The receptor actually consists of two protein chains: one protein chain, known as the IL-9 receptor, binds specifically with IL-9 and the other protein chain is the chain, which is shared in common with the IL-2 receptor..sup.46 In addition, the human IL-9 receptor cDNA has been cloned..sup.46,52,53 This cDNA encodes a 522 amino acid protein which exhibits significant homology to the murine IL-9 receptor. The extracellular region of the receptor is highly conserved, with 67% homology existing between the murine and human proteins. The cytoplasmic region of the receptor is less highly conserved. The human cytoplasmic domain is much larger than the corresponding region of the murine receptor..sup.46
The IL-9 receptor gene has also been characterized..sup.53 It is thought to exist as a single copy in the mouse genome and is composed of nine exons and eight introns..sup.53 The human genome contains at least four IL-9 receptor pseudogenes. The human IL-9 receptor gene has been mapped to the 320 kb subtelomeric region of the sex chromosomes X and y..sup.46 Nonetheless, despite these studies, the art lacks any knowledge of a relation between the IL-9 receptor and atopic allergy, asthma, or bronchial hyperresponsiveness.
Thus, the art lacks any knowledge of how the IL-9 gene, its receptor, and their functions, are related to atopic allergy, asthma, bronchial hyperresponsiveness, and related disorders. Therefore, there is a specific need in the art for genetic information on atopic allergy, asthma, bronchial hyperresponsiveness, and for elucidation of the role of IL-9 in the etiology of these disorders. There is also a need for elucidation of the role of the IL-9 receptor and the IL-9 receptor gene in these disorders. Furthermore, most significantly, based on this knowledge, there is a need for the identification of agents which are capable of regulating the interaction between IL-9 and its receptor for treating these disorders.